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Ian Campbell d4ced2ef77 allow plugins to have argument which match a top-level flag. The issue with plugin options clashing with globals is that when cobra is parsing the command line and it comes across an argument which doesn't start with a `-` it (in the absence of plugins) distinguishes between "argument to current command" and "new subcommand" based on the list of registered sub commands. Plugins breaks that model. When presented with `docker -D plugin -c foo` cobra parses up to the `plugin`, sees it isn't a registered sub-command of the top-level docker (because it isn't, it's a plugin) so it accumulates it as an argument to the top-level `docker` command. Then it sees the `-c`, and thinks it is the global `-c` (for AKA `--context`) option and tries to treat it as that, which fails. In the specific case of the top-level `docker` subcommand we know that it has no arguments which aren't `--flags` (or `-f` short flags) and so anything which doesn't start with a `-` must either be a (known) subcommand or an attempt to execute a plugin. We could simply scan for and register all installed plugins at start of day, so that cobra can do the right thing, but we want to avoid that since it would involve executing each plugin to fetch the metadata, even if the command wasn't going to end up hitting a plugin. Instead we can parse the initial set of global arguments separately before hitting the main cobra `Execute` path, which works here exactly because we know that the top-level has no non-flag arguments. One slight wrinkle is that the top-level `PersistentPreRunE` is no longer called on the plugins path (since it no longer goes via `Execute`), so we arrange for the initialisation done there (which has to be done after global flags are parsed to handle e.g. `--config`) to happen explictly after the global flags are parsed. Rather than make `newDockerCommand` return the complicated set of results needed to make this happen, instead return a closure which achieves this. The new functionality is introduced via a common `TopLevelCommand` abstraction which lets us adjust the plugin entrypoint to use the same strategy for parsing the global arguments. This isn't strictly required (in this case the stuff in cobra's `Execute` works fine) but doing it this way avoids the possibility of subtle differences in behaviour. Fixes #1699, and also, as a side-effect, the first item in #1661. Signed-off-by: Ian Campbell <ijc@docker.com>	2019-03-13 11:28:17 +00:00
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main.go	allow plugins to have argument which match a top-level flag.	2019-03-13 11:28:17 +00:00

Ian Campbell d4ced2ef77 allow plugins to have argument which match a top-level flag.

The issue with plugin options clashing with globals is that when cobra is
parsing the command line and it comes across an argument which doesn't start
with a `-` it (in the absence of plugins) distinguishes between "argument to
current command" and "new subcommand" based on the list of registered sub
commands.

Plugins breaks that model. When presented with `docker -D plugin -c foo` cobra
parses up to the `plugin`, sees it isn't a registered sub-command of the
top-level docker (because it isn't, it's a plugin) so it accumulates it as an
argument to the top-level `docker` command. Then it sees the `-c`, and thinks
it is the global `-c` (for AKA `--context`) option and tries to treat it as
that, which fails.

In the specific case of the top-level `docker` subcommand we know that it has
no arguments which aren't `--flags` (or `-f` short flags) and so anything which
doesn't start with a `-` must either be a (known) subcommand or an attempt to
execute a plugin.

We could simply scan for and register all installed plugins at start of day, so
that cobra can do the right thing, but we want to avoid that since it would
involve executing each plugin to fetch the metadata, even if the command wasn't
going to end up hitting a plugin.

Instead we can parse the initial set of global arguments separately before
hitting the main cobra `Execute` path, which works here exactly because we know
that the top-level has no non-flag arguments.

One slight wrinkle is that the top-level `PersistentPreRunE` is no longer
called on the plugins path (since it no longer goes via `Execute`), so we
arrange for the initialisation done there (which has to be done after global
flags are parsed to handle e.g. `--config`) to happen explictly after the
global flags are parsed. Rather than make `newDockerCommand` return the
complicated set of results needed to make this happen, instead return a closure
which achieves this.

The new functionality is introduced via a common `TopLevelCommand` abstraction
which lets us adjust the plugin entrypoint to use the same strategy for parsing
the global arguments. This isn't strictly required (in this case the stuff in
cobra's `Execute` works fine) but doing it this way avoids the possibility of
subtle differences in behaviour.

Fixes #1699, and also, as a side-effect, the first item in #1661.

Signed-off-by: Ian Campbell <ijc@docker.com>

2019-03-13 11:28:17 +00:00

main.go

allow plugins to have argument which match a top-level flag.

2019-03-13 11:28:17 +00:00